In short: the hall collects no personal data at all. It runs no visitor statistics, shows no advertising, embeds no tracking pixel or third-party script and has no system of user accounts.
What stays on your device
So that a game can be resumed later, the hall writes a handful of entries into local storage: unfinished games and problems, your results against each computer level, solved problems, the dates of daily problems you solved, sound and display preferences, and the lighting you picked. None of it is ever sent anywhere. Wiping this site's stored data from the browser settings deletes all of it.
Server logs
The server that delivers the pages keeps brief technical request logs, such as the requested address and the time, which help with security and with finding faults. They are not combined into profiles and are overwritten after a short period.
Messages
A message sent to our address is read and answered, and used for nothing else.